1. Field of the Invention
The present invention relates to optical elements having resin layers and methods of producing such elements, and more particularly, to a resin-coupled aspherical lens having a glass or plastic base material with a spherical surface or a rough aspherical surface and a resin layer with an aspherical surface, and the method of producing such a lens.
2. Description of Related Art
A known aspherical lens structure is shown in FIGS. 3 and 4. FIG. 3 shows a glass or plastic base material 1 having a spherical surface, and FIG. 4 shows an example of such base material 1 having a rough aspherical surface, as disclosed in Japanese Laid-Open Patent Application No. 63-157103.
With the conventionally known aspherical surface, thin (5-100 .mu.m) resin layer 2 is layered on glass or plastic base material 1. With the method generally used for producing this kind of aspherical lens, resin layer 2 is formed using ultraviolet-hardening resin.
With this method of formation it is easy to obtain an aspherical lens having an optical surface of a desired shape, because the optical surface is formed using a malleable ultraviolet-hardening resin fluid. This method lends itself well to mass production. An example of this conventionally known method of producing resin-coupled aspherical lenses is shown in FIGS. 5A-5E for cases in which glass base material 1 possesses a spherical surface.
First, the spherical glass lens (FIG. 5A) is produced using common base material production methods. Melted glass is shaped by pressing, and the resulting glass block is manufactured into a lens having the desired spherical surface by machine processing. Next, reflection-preventing membrane 4 is coated on one surface of the lens produced by the base material production process, by a reflection-preventing membrane formation process (FIG. 5B). Furthermore, by a resin layer formation process (FIG. 5C), an ultraviolet-hardening resin fluid is coated on the surface of the base material on which reflection-preventing membrane 4 is formed by the reflection-preventing membrane formation process. The resin fluid coating forms resin layer 2. The surface on which resin layer 2 is formed will be referred to hereafter as the front surface of the lens. After formation of resin layer 2, reflection-preventing membrane 5 is coated on the front surface, on which resin layer 2 is formed, by a front surface reflection-preventing membrane formation process (FIG. 5D). Lastly, during a light-shielding membrane formation process (FIG. 5E), a light-shielding coating is applied so as to cover the outermost perimeter of the lens, that is, the rough edge area, and the outer perimeter of reflection-preventing membrane 5. The coating is baked on to form light-shielding membrane 3. When black ink is used as the light-shielding coating, it is not heated but rather is allowed to dry naturally.
The edge of the lens produced using this method is shown in FIG. 2. With conventional methods of production, after resin layer 2 has been formed, reflection-preventing membrane 5 is coated onto the surface of resin layer 2, following which light-shielding membrane 3 is formed on the outer perimeter, that is, the rough area, of the lens and the outermost perimeter of reflection-preventing membrane 5. Consequently, the edge of resin layer 2 is covered by the reflection-preventing membrane 5.
However, with a resin-coupled aspherical lens produced using the described production process, edge surface 6 of the outermost perimeter of resin layer 2 shines in a ring-like manner when viewed from the back surface of the lens (the surface on which resin layer 2 is not formed). This condition is shown in FIGS. 8A-8C. Each of the FIGS. 8A-8C shows the area around the perimeter of a lens produced using conventional technology, as viewed from the back surface. FIG. 8A is magnified 10 times, FIG. 8B 20 times and FIG. 8C 40 times. In addition, FIGS. 9A-9C are photographs of the area around the perimeter of a lens produced using conventional technology, the photograph being taken from the back surface. FIG. 9A is magnified 10 times, FIG. 9B 20 times and FIG. 9C 40 times.
In both FIGS. 8A-8C and FIGS. 9A-9C, outer perimeter E of the lens, in which the edge surface of the outermost perimeter of resin layer 2 is reflective, and a ring-like region of light r are observable. With this ring-like region of light r, reflection is not uniform, as spots w are visible and form knots in the ring. This kind of ring-like and non-uniform reflection give a poor outer appearance, which, in some cases, is undesirable. When viewed through the lens, the reflection from edge surface 6 of the outermost perimeter of resin layer 2 is close to complete reflection and is seen as an extremely bright light. Furthermore, it is positioned in a place where reflection of the penetrating light stands out easily.